There is known, in particular from EP Patent No 607 828, an electromagnetic timepiece motor comprising a stator, a rotor and a frame made of synthetic material. This frame comprises two distinct pieces respectively forming a case with two apertures and a cover arranged for closing the first of the two apertures. The first aperture is provided for the insertion of the rotor into the case. The cover includes a bearing. The second aperture is a lateral aperture arranged to enable a wheel to mesh with the pinion of the rotor housed in the frame.
The rotor is assembled in the frame by inserting the rotor into the case through the first aperture until a rotor pivot reaches the bottom of the case, and then further while ensuring that the pivot is aligned with the bearing arranged in the bottom. Next, the cover is provided and fixedly arranged so as to close the first aperture while ensuring that the rotor is held in a centred position so that the second rotor pivot penetrates the cover bearing.
The method of manufacturing the frame-rotor assembly disclosed in EP Patent No 607 828 has several drawbacks. Firstly, the frame must be made in two parts with a closing cover. Further, it is difficult to arrange the rotor in the frame. The insertion of the first pivot into the bearing at the bottom of the case not only requires precise handling of the rotor when it is inserted into the case, but the insertion of the second pivot into the cover bearing poses a serious problem.
There is known from JP Patent No 2006-226771 a timepiece movement with a motor having a rotor whose two pivots are inserted into two respective bearings. The first bearing is formed in one portion of the bottom plate of the movement whereas the second bearing is formed in a portion of a bridge of said movement. The rotor is assembled in a conventional manner, i.e. in a similar manner to the assembly of a wheel between the bottom plate and a bridge. This document proposes to form the parts defining the first and second bearings from flat springs operating as shock absorbers in the event of a shock in the direction of the rotor axis. It will be noted that the assembly of a rotor without a frame is difficult and that the only function of the flat springs is to protect the motor in the event of shocks.